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Guidelines for Thermoplastic Color Control and Change Management

Sunday, 01 April 2012

Page 2 of 2

Fig. 2 illustrates a color control scenario
with a numeric limitation in CIE
L*a*b* color space of 1.0 unit for L*, a*
and b* along with a color representation
of each. When setting up a color control
program, care should be taken not to
establish color acceptability limits
beyond what is necessary for the usage
situation. Depending on the color difference
equation used, it will not be unusual
to have different limits set for each
variable. It is common to have more
color rejects and returns as well as
increased production costs when using
extremely tight color tolerances.

Color control programs can be very
detailed depending on the color requirements of an application. For help
with setting up a color control program,
ASTM International (http://www.astm.org/index.shtml) has several methods and standard
practices for evaluating color and for
establishing color tolerances and color differences
based on visual evaluations and
from instrumental color measurements.
Color measuring instrument manufacturers
can also help with establishing color
controls with the purchase of hardware
and software.

Finally, it is important that standards,
measuring requirements, and established
tolerances are communicated
and understood throughout
your supply chain for any
color control program to be successful.
A good color control
program will help make the regulatory
approval process easier
and less time-consuming for all
involved.

Sterilization Techniques’
Effect on Color

An issue to be aware of during
medical device development is the
effect sterilization may have on the
color of plastic components. The
most commonly used sterilization
techniques are autoclave, ethylene
oxide gas (EtO), and radiation
sterilization by either gamma or E-beam
radiation. Each sterilization
technique has an effect on plastic
materials that may adversely affect
the color and physical properties.
It is recommended to check color
in the finished assembled state
before and after sterilization to
determine the visual and physical
effects.

Autoclave – Typical reactions to
autoclave may include hydrolysis,
warp, and part distortion/deformation;
however, color is usually
not affected.

EtO is often used for heat-sensitive
polymers and usually
does not cause significant color
change.

Gamma and E-Beam radiation
sterilization can cause cross-linking
of polymers, chain scission
and yellowing of colors. Although
not the subject of this technical
brief, there are techniques that
knowledgeable color suppliers
use to stabilize colors against radiation.

Conclusion

Increased regulatory scrutiny placed on
colored plastics from Europe, Japan, the
United States, and other countries to pass
biologic testing makes material and color
selection a critical skill when developing new
medical devices. Selecting a color compounder
with a long history of success in the
medical device market is critical as they will
have important services such as ISO 10993
resin and pigment selections, resin and color
advice based on experience, formulation
control, and change management services.

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